Catalyst layers of membrane-electrode assemblies and methods of making same

ABSTRACT

Improved catalyst layers for use in fuel cell membrane electrode assemblies, and methods for making such catalyst layers, are provided. Catalyst layers can comprise structured units of catalyst, catalyst support, and ionomer. The structured units can provide for more efficient electrical energy production and/or increased lifespan of fuel cells utilizing such membrane electrode assemblies. Catalyst layers can be directly deposited on exchange membranes, such as proton exchange membranes.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. Ser. No. 16/891,506 entitled“Catalyst Layers of Membrane-Electrode Assemblies and Methods of MakingSame” filed on Jun. 3, 2020. U.S. Ser. No. 16/891,506 is a continuationof U.S. Ser. No. 16/890,269 filed on Jun. 2, 2020, now U.S. PatentApplication Publication 2020/0365909 entitled “Catalyst Layers ofMembrane-Electrode Assemblies and Methods of Making Same.” U.S. Ser. No.16/890,269 is a continuation of PCT Application No. PCT/US20/30234entitled “Catalyst Layers of Membrane-Electrode Assemblies and Methodsof Making Same” filed on Apr. 28, 2020. PCT Application No.PCT/US20/30234 claims priority to and the benefit of U.S. ProvisionalApplication No. 62/847,156 entitled “Catalyst Layers ofMembrane-Electrode Assemblies and Methods of Making Same” filed on May13, 2019. Each of the foregoing applications are hereby incorporated byreference in their entirety (except for any subject matter disclaimersor disavowals, and except to the extent of any conflict with thedisclosure of the present application, in which case the disclosure ofthe present application shall control).

TECHNICAL FIELD

The disclosure relates generally to systems, methods, and devices forfuel cell components, and more particular1y, to methods, systems, anddevices for fuel cell membrane-electrode assemblies.

BACKGROUND

Current state-of-the-art catalyst layers in membrane-electrodeassemblies (MEAs) used in fuel cells (such as proton exchange membranefuel cells) are formed utilizing either slot-die coating or spraycoating of an intermediate substrate (such as a decal substrate). Thesemethods of deposition require solvent drying steps which cause unevencatalyst layer surfaces due to capillary forces originating fromevaporation. These forces may directly cause cracks (desiccationstructures) to form in the catalyst layer. However, even in catalystlayers without any directly-formed cracks, the thinnest portions ofthese surfaces provide nucleation sites for crack growth during normaloperation of the fuel cell MEA. Once a crack is formed in the catalystlayer, the crack will propagate into the membrane, causing pin-holes andfailure of the MEA.

Another shortcoming of current methods of forming catalyst layers isover-use of ionomer to obtain adequate ionic conductivity within thecatalyst layer. Several deleterious effects are observed when excessionomer is present, including binding of ionomer to catalyst sites. Whenionomer is bound to catalyst surfaces, sulfonate-ion poisoning occurs,reducing oxygen reduction reaction kinetics, and the bound ionomerstiffens, increasing Knudsen-dominated gas transport effects. Anothernegative effect of excess ionomer is an overall increase in catalystlayer hydrophilicity, which dissolves metal catalyst and hastensdegradation. In light of these and other shortcomings of currentapproaches, catalyst layers having reduced ionomer usage and crackformation and propagation during operation of the fuel cell aredesirable.

SUMMARY

In an exemplary embodiment, a method of forming an electrode comprisesproviding a first reservoir containing a first dispersion, wherein thefirst dispersion comprises an ionomer, a carbon-containing catalystpowder, and a first solvent; providing a second reservoir containing asecond dispersion, wherein the second dispersion comprises the ionomerand a second solvent; applying an electrical bias between a substrateand a first needle in fluid communication with the first reservoir; andpumping the first dispersion from the first reservoir through the firstneedle towards a first surface of the substrate and pumping the seconddispersion from the second reservoir through the first needle towardsthe surface of the substrate to form a plurality of structured units ona surface of the substrate. Each of the structured units comprise aspherical inner core having a first radius and a spherical outer shellhaving a second radius greater than the first radius and concentricallysurrounding the inner core, and the outer shell comprises the ionomer ata first concentration and the inner shell comprises the ionomer at asecond concentration that is greater than the first concentration.

In another exemplary embodiment, a method of forming an electrodecomprises providing to a first reservoir a first dispersion comprising aplurality of catalyst particles, a surfactant, a first solvent, andwater; providing to a second reservoir a second dispersion comprising anionomer and a second solvent; applying an electrical bias between thesubstrate and a first needle in fluid communication with the firstreservoir and a second needle in fluid communication with the secondreservoir; pumping the first dispersion through the first needle towardsa surface of a substrate; and pumping the second dispersion through thesecond needle towards the surface of the substrate.

The foregoing features and elements may be combined in any combination,without exclusivity, unless expressly indicated herein otherwise. Thesefeatures and elements as well as the operation of the disclosedembodiments will become more apparent in light of the followingdescription and accompanying drawings. The contents of this section areintended as a simplified introduction to the disclosure and are notintended to be used to limit the scope of any claim.

BRIEF DESCRIPTION OF THE DRAWINGS

Non-limiting and non-exhaustive embodiments of the present disclosureare described with reference to the following figures, wherein likereference numerals refer to like parts throughout the various viewsunless otherwise specified. Advantages of the present disclosure willbecome better understood with regard to the following description andaccompanying drawings where:

FIG. 1A is a cross-sectional view of an exemplary membrane-electrodeassembly in accordance with various exemplary embodiments;

FIG. 1B is a cross-sectional view of an exemplary membrane-electrodeassembly in accordance with various exemplary embodiments;

FIG. 2A is a schematic view of an exemplary structured unit of acatalyst layer in accordance with various exemplary embodiments;

FIG. 2B is a cross-sectional view of an exemplary structured unit of acatalyst layer in accordance with various exemplary embodiments;

FIG. 3 is a perspective view of an exemplary structured unit of acatalyst layer showing a portion of an outer shell removed, inaccordance with various exemplary embodiments;

FIG. 4A is a graphical representation of a number of different relativeionomer concentration profiles in accordance with various exemplaryembodiments;

FIG. 4B is a close up of section “A” of the graphical representation ofa number of different relative ionomer concentration profiles of FIG.4A;

FIG. 5 illustrates an exemplary method of making a catalyst layer inaccordance with various exemplary embodiments;

FIG. 6 illustrates another exemplary method of making a catalyst layerin accordance with various exemplary embodiments;

FIG. 7 illustrates yet another exemplary method of making a catalystlayer in accordance with various exemplary embodiments; and

FIG. 8 illustrates an exemplary method of making a membrane-electrodeassembly in accordance with various exemplary embodiments.

DETAILED DESCRIPTION

For purposes of promoting an understanding of the principles inaccordance with the disclosure, reference will now be made to theembodiments illustrated in the drawings and specific language will beused to describe the same. It will nevertheless be understood that nolimitation of the scope of the disclosure is thereby intended. Anyalterations and further modifications of the inventive featuresillustrated herein, and any additional applications of the principles ofthe disclosure as illustrated herein, which would normally occur to oneskilled in the relevant art and having possession of the disclosure, areto be considered within the scope of the disclosure.

It is to be understood that this disclosure is not limited to theparticular configurations, process steps, and materials disclosed hereinas such configurations, process steps, and materials may vary. It isalso to be understood that the terminology employed herein is used forthe purpose of describing particular embodiments only and is notintended to be limiting. In describing the disclosure, the followingterminology will be used in accordance with the definitions set outbelow. As used in this specification and the appended claims, thesingular forms “a,” “an,” and “the” include plural referents unless thecontext clear1y dictates otherwise. As used herein, the terms“comprising,” “including,” “containing,” “characterized by,” andgrammatical equivalents thereof are inclusive or open-ended terms thatdo not exclude additional, unrecited elements or method steps.

Via application of principles of the present disclosure, exemplarycatalyst layers can increase the lifespan of a fuel cell by preventingcatastrophic failure of the membrane. Further, exemplary catalyst layersprovide sufficient space between spherical sub-structures to expand andcontract which further protect against cracking due to normal operation.Additionally, exemplary catalyst layers provide more optimal utilizationof catalyst material, potentially providing higher power at high voltage(i.e. high efficiency), and reducing waste heat.

With reference to FIGS. 1A and 1B, in various embodiments, amembrane-electrode assembly 100 is illustrated. MEA 100 comprises a pairof electrodes 104 a and 104 b positioned on either side of and affixedto an exchange membrane 102. In various embodiments, MEA 100 is amembrane-electrode assembly used in a fuel cell, such as a protonexchange membrane-based fuel cell.

In various embodiments, electrode 104 a and/or 104 b comprises acatalyst layer 180. Catalyst layer 180 catalyzes an electrochemicalreaction or reactions that convert chemical constituents and generateelectrical energy. For example, catalyst layer 180 can provide catalyticsupport for electrode reactions which occur in MEA 100.

In various embodiments, electrode 104 a is operable as an anode. Ananodic reaction can occur within electrode 104 a, such as the oxidationof a fuel source. For example, the oxidation reaction can comprise thedisassociation of protons and electrons from a diatomic hydrogenmolecule. In such embodiments, catalyst layer 180 of electrode 104 afacilitates the oxidation of diatomic hydrogen gas by providingcatalytic support for the anodic reaction.

Further, in various embodiments electrode 104 b is operable as acathode. A cathodic reaction can occur within electrode 104 b, such asthe reduction of oxygen. For example, the reduction of oxygen in cathode104 b can comprise the combination of protons, electrons, and diatomicoxygen to form water molecules. In such embodiments, catalyst layer 180of electrode 104 b facilitates formation of water by providing catalyticsupport for a cathodic reaction.

In various embodiments, catalyst layer 180 comprises electrically-activecatalyst particles that facilitate the anodic and/or cathodic reactionoccurring in electrodes 104 a and/or 104 b. For example, catalystparticles can comprise electrically-active platinum group metals, suchas platinum, non-platinum group metal transition-metal-basedn4-macrocyclic metal complexes, and/or the like. Although described withreference to specific catalyst particles, any suitable catalystparticles capable of catalyzing anodic or cathodic reactions within anMEA are within the scope of the present disclosure.

In various embodiments, catalyst layer 180 further comprises supportparticles onto which the individual catalyst particles are adhered andthereby supported. In various embodiments, for example, supportparticles can comprise carbon-based particles having average sizes thatare larger than the average size of the catalyst particles. In variousexemplary embodiments, catalyst particles can range in size from 1 nm to10 nm in the longest dimension. Moreover, support particles can range insize from 30 nm to 200 nm in the longest dimension. In one exemplaryembodiment, catalyst particles having a size of 4 nm in the longestdimension are adhered to a support particle having a size of 50 nm inthe longest dimension. Moreover, multiple catalyst particles can beadhered to and thus supported by a single support particle. For example,a single support particle may have 1, 2, 3, 5, 10, 20, 50, 100, or evenmore catalyst particles adhered thereto.

In various embodiments, the support particles comprise a carbon-basedarticle or material such as one or more of paracrystalline carbon (e.g.,carbon black), carbon nanotubes, diamond, graphite, graphene, tungstencarbide, silicon carbide, and/or the like. Additionally, the supportparticles may comprise articles or materials not including carbon, suchas one or more of titanium dioxide, iridium oxide, tungsten oxide, tinoxide, niobium oxide, and/or the like. Although described with referenceto specific materials, any suitable support particle (or combination,blend, or mixture of particles) capable of supporting catalyst particleswithin catalyst layer 180 is within the scope of the present disclosure.

Support particles and electrically-active catalyst particles can beprovided together, for example in a commercially-available mixture. Theuse of catalyst inks, catalyst powders, or other mixtures of supportparticles and catalyst particles is within the scope of the presentdisclosure. Stated another way, catalyst layer(s) 180 in accordance withvarious exemplary embodiments can be prepared using individual chemicalcomponents or mixtures of chemical components.

In various embodiments, catalyst layer 180 comprises a proton-conductingionomer. The combined catalyst particles and support particles may beimpregnated with the proton-conducting ionomer to facilitate transportof protons through catalyst layer 180 and towards, for example, a protonexchange membrane 102. Suitable proton-conducting ionomers includeperfluorosulfonic acid (PFSA), sulfonated tetrafluoroethylene basedflouropolymers (such as Nafion®, sold by The Chemours Company),perfluoro imide acids (PFIA), hydrocarbon-based ionomers, and/or thelike.

In other embodiments, catalyst layer 180 comprises an anion-conductingpolymer. For example, catalyst layer 180 may be utilized in an anionexchange membrane, and comprise an ionomer such as short, medium, and/orlong side chain quaternary polyphenylene oxides (QPPO), among otherssuitable for use in an anion exchange membrane. The use of any suitableionomer is within the scope of the present disclosure.

In various embodiments, catalyst layer 180 can comprise one or morelayers of structured units 106. In catalyst layer 180, structured units106 may be arranged generally in over1apping planes, for example planesof generally spherical structured units 106 such that structured units106 of one plane are positioned generally at least partially withinvoids between structured units 106 of another plane. In this manner, thedensity of structured units 106 in catalyst layer 180 is increased. Inother exemplary embodiments, structured units 106 may be dispersedgenerally at random in catalyst layer 180. Moreover, structured units106 may be disposed and/or positioned in catalyst layer 180 in anysuitable manner.

With momentary reference to FIG. 1B, in some exemplary embodimentscatalyst layer 180 comprises at least one layer of structured units 106having a first size, and a second layer of structured units 106 having asecond, different size. For example, structured units 106 disposed in alayer generally adjacent to (and/or close to) exchange membrane 102 maybe smaller, resulting in a higher number of connected ionic channels.Moreover, structured units 106 disposed in a layer generally adjacent to(and/or close to) a micro-porous layer 108 may be larger, resulting inlarger channels for gas to enter. While the example shown in FIG. 1Billustrates a single layer of smaller structured units 106 and a singlelayer of larger structure, it will be appreciated that multiplesub-layers may exist in each such layer therein, and/or that repeatingand/or alternating patterns of layers having differing sizes and/orshapes of structured units 106 may be utilized.

With initial reference to FIGS. 2A and 2B, structured units 106 cancomprise a core-and-shell type structure. For example, structured units106 can comprise a shell 210 surrounding a core 212. In variousembodiments, structured units 106 comprise an approximately sphericalshape having a radius r2. In other embodiments, structured units 106comprise a non-spherical shape having an effective radius of r2. Fornon-spherical shapes, effective radius r2 can be calculated orapproximated as:

${r2} = \sqrt{\left( \frac{A}{4\pi} \right)}$

where A is the surface area of the non-spherical shape.

For illustrative purposes, structured units 106 will be furtherdescribed in reference to a spherical shape with a radius of r2.However, it will be understood that structured units 106, including oneor more individual components of structured units 106 such as shell 210and core 212, can comprise other three-dimensional shapes as well, suchas ovoid shapes, polyhedra, irregular shapes, and/or the like.

In various embodiments, core 212 comprises a sphere having a radius ofr1. Shell 210 comprises a spherical outer layer surrounding core 212 andhaving a thickness of r2-r1 (e.g., shell 210 is configured as aspherical shell considered to begin at r1 and extending to r2). Invarious embodiments, r2 is between 35 nanometers and 1,600 nanometers.In various embodiments, r1 is between 25 nanometers and 1,500nanometers.

Core 212 can comprise, include, and/or contain a number of supportparticles 222. In various embodiments, support particles 222 areconfigured with an average length, in a longest dimension, of between 60nanometers and 200 nanometers. For support particles 222 having agenerally spherical shape, support particles 222 may be configured witha radius of between 30 nanometers and 100 nanometers.

One or more catalyst particles 224 can be physically adhered to andsupported by a corresponding support particle 222. Catalyst particles224 may be adhered to a support particle 222 in any suitable manner, forexample via van der Waals forces.

In various embodiments, core 212 further comprises, includes, and/orcontains at least one ionomer 220 a. For example, ionomer 220 a can atleast partially surround support particles 222 and catalyst particles224. Ionomer 220 a can comprise any suitable proton-conducting ionomer,such as a sulfonated tetrafluoroethylene-based fluoropolymer. In variousembodiments, core 212 comprises an overall ratio of ionomer to carbon ofbetween 0.01 and 0.5. “Ionomer to carbon ratio” (or “I/C ratio”) is acommonly used term in the design of catalyst layers and is a relativemeasure of the amount of ionomer compared to the amount of carbonsupport (i.e., support particles 222) for the catalyst (i.e., catalystparticles 224). If the percentage of catalyst support is known, the I/Cratio may also be determined. The I/C ratio may also be utilized forcatalysts that do not contain carbon, or catalysts that are PGM-free(which contain C-N structures). Stated another way, core 212 cancomprise more of support particles 222 and catalyst particles 224 thanionomer 220 a (for example, core 212 may comprise between 50% and 60%,or further, 55% of support particles 222, between 35% and 40%, orfurther, 37% of catalyst particles 224, and 5% of ionomer 220 a,resulting in an I/C ratio of approximately 0.1, where the foregoingpercentages are in terms of mass). In a contrasting example, anexemplary shell 210, having an I/C ratio of approximately 10, maycomprise 8.6% of support particles 222, 5.7% of catalyst particles 224,and 85.7% of ionomer 220 a by mass and may be formed utilizing acatalyst powder comprising 40% platinum and 60% carbon.

Shell 210 can comprise a second ionomer 220 b. In various embodiments,second ionomer 220 b is the same ionomer as 220 a of core 212. In otherembodiments, ionomer 220 a and 220 b are different ionomers. Moreover,three or more ionomers may also be utilized, for example in order toachieve a desired performance characteristic, cost, or other aspect ofthe overall ionomer component. In various embodiments, shell 210 cancomprise an overall ratio (i.e., summing all ionomers present) ofionomer to carbon of between 0.7 and 5.0.

Conventionally, excess ionomer is typically included in a catalyst layerto ensure adequate conductivity within the catalyst layer. Specifically,the non-uniform distribution of catalyst particles and support particlesmay necessitate excess ionomer use in the catalyst layer. However,excessive ionomer can cause bonding of the ionomer to catalyst surfaces,causing sulfonate-ion poisoning of catalyst sites. Such poisoning of thecatalyst can reduce oxygen reduction reaction kinetics. The ionomerbound to the catalyst surface can also stiffen, increasingKnudsen-dominated gas transport effects. Further, excess ionomer cancause an overall increase in the hydrophilicity of the catalyst layer.

Accordingly, in various embodiments, utilizing principles of the presentdisclosure (for example, by providing core 212 having a first I/C ratiosurrounded by a shell 210 having a second I/C ratio that is higher thanthe first I/C ratio) can more effectively and optimally utilize ionomer.For example, this approach creates “reservoirs” of protons that increasethe ionic conductivity of water within the catalyst layer (through whichthe Grotthuss mechanism or vehicular mechanism will transport protons tocatalytic sites of catalyst particles 224 within core 212) withoutincreasing poisoning of the catalyst surface and/or without increasinggas transport resistance. Structured units 106 can, for example, improvecatalyst utilization by producing more electrical current with the samecatalyst content, or requiring less catalyst to produce the sameelectrical current. Additionally, a smaller amount of total ionomer maybe utilized, reducing overall hydrophilicity and improving durability ofthe catalyst layer.

An I/C ratio can be determined, calculated, and/or measured atparticular points or radii within structured units 106. For example, invarious embodiments the I/C ratio of core 212 at or near r1 is between0.1 and 0.9. Further, in various embodiments the I/C ratio of shell 210at or near r2 is between 0.9 and 5. In various embodiments, the I/Cratio of shell 210 (e.g., between r1 and r2 of structured unit 106) ishigher than the I/C ratio of any point in core 212 (e.g., at any pointbetween the effective center of structured unit 106 and r1).

With momentary reference now to FIG. 3, in various exemplary embodimentsshell 210 may have a generally constant thickness (i.e., a thicknessvarying by +/−10%), wherever on structured unit 106 the thickness ismeasured. However, it will be appreciated that process variations,material differences, structured unit 106 geometry, and/or the like mayresult in configurations where shell 210 varies in thickness dependingon the location on structured unit 106 where the thickness is measured.All such variations, combinations, and configurations are considered tobe within the scope of the present disclosure.

With initial reference to FIGS. 4A and 4B, various I/C profiles of anexemplary structured unit 106 are graphically represented. In variousembodiments, the I/C ratio within core 212 increases from a first valueat or near the effective center of structured unit 106 and increases toa second, larger value at or near r1. The I/C ratio within shell 210 mayincrease from a third value at or near r1 to a fourth, larger value ator near r2. For example, when graphically represented, the I/C ratiofrom the effective center of structured unit 106 to a radius at or nearr2 comprises (or may be represented by) a sigmoidal function. In variousembodiments, r1 is the point in structured unit 106 at which aninflection point of the function representing the I/C ratio occurs. Aninflection point is a point in a given function (such as a sigmoidalfunction) where the function changes from convex to concave (or viceversa); at an inflection point, the third derivative of the function iszero. Stated another way, in various exemplary embodiments core 212ends, and shell 210 begins, at an inflection point of a functionrepresenting the I/C ratio.

For example, an I/C ratio profile 490 can comprise (or be representedby) a sigmoidal function that starts at a minimum value 499 a (forexample, at the center of a structured unit 106) and approaches (orreaches) a maximum value 497 a at r2. In various embodiments, minimumvalue 499 a is greater than zero and can be between 0.01 and 0.5, andpreferentially, between 0.1 and 0.4. Further, maximum value 497 a can bebetween 0.7 and 5.0, and preferentially, between 1 and 2.

I/C ratio profile 490 can further comprise, for example, an inflectionpoint at r1 having a tangent 495 a. In various embodiments, tangent 495a has a slope relative to a horizontal axis 493 of greater than 1.0.

Another I/C ratio profile 492 can comprise (or be represented by) asigmoidal function that starts at a minimum value 499 a and approaches amaximum value 497 a at r2. In various embodiments, minimum value 499 ais greater than zero and can be between 0.01 and 0.5, andpreferentially, between 0.1 and 0.4. Further, maximum value 497 a can bebetween 0.7 and 5, and preferentially, between 1.0 and 2.0. I/C ratioprofile 492 further comprises, for example, an inflection point at r1having a tangent 495b. In various embodiments, tangent 495 b has a sloperelative to horizontal axis 493 of greater than 1.0, but lower than theslope of tangent 495 a of I/C ratio profile 490.

Yet another I/C ratio profile 494 can comprise (or be represented by) asigmoidal function that approximates a step function. In variousembodiments, I/C ratio profile 494 starts at a minimum value 499 a andends at a maximum value 497 a at r2, with an inflection point at r1having a slope relative to a vertical axis 491 of between 0.1 and zero.In such embodiments, the I/C ratio is near1y constant (i.e., within 10%)at or near minimum value 499 a from the effective center of structuredunit 106 to r1, then increases from minimum value 499 a to maximum value497 a at r1 (i.e., within 10% of 497 a). Stated another way, core 212comprises a constant (and/or varying less than 10%) first I/C ratio, andshell 210 comprises a constant (and/or varying less than 10%) second andhigher I/C ratio.

Still another exemplary I/C ratio 496 can comprise (or be representedby) a sigmoidal function that starts at a minimum value 499 b andapproaches (or reaches) a maximum value 497 b at r2. In variousembodiments, minimum value 499 b is greater than zero and can be between0.01 and 0.5, and preferentially, between 0.1 and 0.4. Further, maximumvalue 497 a can be between 0.7 and 5.0, and preferentially, between 1.0and 2.0.

I/C ratio profile 496 can further comprise, for example, an inflectionpoint at r1 having a tangent 495 d. In various embodiments, tangent 495a has a slope relative to horizontal axis 493 of greater than 1.0, butlower than such slope of tangent 495 a and/or tangent 495 b of I/C ratioprofiles 490 and 492 respectively.

Exemplary I/C profiles 490, 492, 494, and 496 illustrate variousconfigurations of structured units 106, including the I/C profiles ofcorresponding cores 212 and shells 210. Any suitable combination of I/Cprofiles, including various minimum values, maximum values, inflectionpoint tangent slope values, profile characteristics between a minimumvalue and an inflection point, and profile characteristics between aninflection point and a maximum value, are within the scope of thepresent disclosure.

In various embodiments, catalyst layer 180 comprising structured units106 may comprise or be configured with a higher number (and/or higherconcentration) of primary pores than conventional catalyst layers.Because a smaller amount of ionomer is used in structured units 106,more primary pores may be available for improved transport (for example,of water) within catalyst layer 180. In various embodiments, structuredunits 106 allow for improved ionic conductivity of catalyst layer 180over conventional designs because the increased number of smaller,primary pores allows for capillary condensation of water.

Additionally, in various embodiments catalyst layer 180 can comprise orbe configured with macro pores. For example, structured units 106 can bespaced along a layer of catalyst layer 180 such that there is spacebetween the structured units 106 that can be described as macro pores ortertiary pores. Such a pore distribution can reduce flooding of catalystlayer 180 at high relative humidities (for example, relative humiditiesabove 80%) by providing for improved water management through catalystlayer 180 (as compared to conventional catalyst layer designs). Improvedwater management through catalyst layer 180 can provide for longer lifespan and/or more efficient operation of catalyst layer 180, and in turn,an MEA in which catalyst layer 180 is utilized. Further, configuringcatalyst layer 180 with macro pores as contemplated in various exemplaryembodiments improves oxygen diffusivity.

In various exemplary embodiments, catalyst layer 180 is configured with(and/or achieves or exhibits) improved resistance against crackingduring operation. Cracking of the catalyst layer of an MEA is a primarymode of failure. For example, in conventional catalyst layer designs,expansion and contraction of the catalyst layer (corresponding withincreasing and decreasing relative humidity within the catalyst layerduring operation) can propagate cracks within the catalyst layer. Invarious embodiments, the physical structure of structured units 106provides for improved expansion and contraction during operation. Thisis due at least in part to structured units 106 being more uniform thanconventional catalyst layer agglomerates and therefore the space betweenthese units is more uniform as well; combined with the fact that thevoid spaces will simply be larger yields the ability to swell uniformlyinto these larger spaces and reduce and/or prevent catastrophic catalystlayer failure (i.e. cracking). Thus, application of principles of thepresent disclosure ensures that cracks are less likely to form andpropagate through catalyst layer 180. This improved performanceincreases the life span of catalyst layer 180.

In various embodiments, core 212 and/or shell 210 comprise one or moreadditives. For example, additives can include chemical constituents thatimpart a benefit or increase in performance of core 212 and/or shell210, such as improved stability, rigidity, transport of chemicalreactants or products of electrochemical reactions, or other parametersof catalyst layer 180. Suitable additives can comprise one or more of ahydrophobic polymer (e.g., polyvinylidene fluoride or acids formed fromthis polymer), a radical scavenging ion or compound (e.g. cerium oxide,CeO₂), hydrophobic powders (e.g. Teflon-coated carbon), and/or othersuitable additives or combinations of additives. In various embodiments,an additive can comprise a concentration of between 0.01% and 10% incore 212 and/or shell 210 by mass.

Core 212 and shell 210 can comprise and/or be configured with differentconcentrations of a similar or identical additive. Alternatively, core212 and shell 210 comprise and/or are configured with differentadditives and/or additive concentrations. In yet other embodiments, onlyone of core 212 or shell 210 comprises or is configured with one or moreadditives. Although described with reference to particular embodiments,any combination of suitable additives in core 212 and/or shell 210 iswithin the scope of the present disclosure.

Table 1 illustrates exemplary characteristics of catalyst layer 180,including structured units 106, in accordance with various embodiments.

TABLE 1 Parameter Range Core Overall I/C Ratio   0-1 Shell Overall I/CRatio 0.5-100 Catalyst Type PGM-based, PGM-alloy, and/or PGM-freeCatalyst Support Type Carbon blacks, carbon nanotubes, diamond,graphite, graphene, silicon carbide, titanium dioxide, iridium oxide,tungsten oxide, tin oxide, niobium oxide, tungsten carbide Ionomer TypePerfluorosulfonic acid (PFSA), Perfluoro Imide Acids (PFIA),hydrocarbon-based. Long side chain, medium side chain, short side chain,quaternary polyphenylene oxide (QPPO) Ionomer Counter-ion H⁺, Na⁺, Li⁺,K⁺, Cs⁺ Ionomer EW 600 EW-1200 EW Solid % in “core solution/dispersion”  1%-25% Solid % in “shell solution/dispersion”   1%-50% AdditivesPolyvinylidene fluoride (and other hydrophobic polymers), cerium (andother radical scavenging compounds) Additive concentration range0.01%-5% r1 25 nm-1.5 micron r3 10 nm-100 nm (thickness of shell 210) r235 nm-1.6 micron

With reference now to FIG. 5, a method 500 for forming a catalyst layerof structured units in accordance with various exemplary embodiments isillustrated. Method 500 can, for example, form a catalyst layer 180 foruse in an MEA.

In various embodiments, method 500 utilizes an electrospraying processto form a catalyst layer (such as catalyst layer 180) comprising one ormore vertically-stacked layers of structured catalyst units (such asstructured units 106). For example, electrospraying can comprisespraying one or more ion-containing dispersions in an electric field toform relatively or substantially spherical units or particles. As willbe described in detail, an electrical bias can be applied between theneedle through which the dispersions are sprayed and a substrate ontowhich the dispersion is to be adhered. As the dispersion exits theneedle, a taylor cone is formed, creating a liquid jet of thedispersion. As the jet travels towards the substrate, the ioniccomponents of the dispersion are drawn towards the outside surface ofthe jet. In various embodiments, the core and shell structure are formedas one or more dispersions exit the needle, pass through the electricfield, and deposit on the substrate.

In various embodiments, method 500 comprises a step 530 of positioning asubstrate relative to a first needle of an electrospray apparatus. Invarious embodiments, method 500 comprises depositing a catalyst layer onan intermediate substrate, commonly referred to as a decal transfertechnique. For example, the intermediate substrate can comprise a decalonto which a catalyst layer is deposited. As will be discussed further,the decal can then be used to transfer the catalyst layer to an exchangemembrane. Conventional methods of forming an MEA utilize a decaltransfer method because exchange membranes (such as proton exchangemembranes) can be negatively impacted by solvent, and therefore areunsuitable substrates for deposition techniques that apply “wet” (i.e.,solvent-containing) catalyst layers to substrates.

In other embodiments, in contrast to conventional techniques for formingMEAs, method 500 comprises direct deposition of catalyst layer 180 ontoan exchange membrane (such as a proton exchange membrane). For example,as will be discussed in greater detail, because structured units 106 andcatalyst layer 180 are substantially free from solvent (i.e., comprisingless than 1% of solvent by mass, or further, less than 0.1% of solventby mass), catalyst layer 180 can be directly applied to an exchangemembrane. This allows for faster, simpler, and/or lower-costmanufacturing.

Any suitable substrate (including gas diffusion layers and othersubstrates utilized in fuel cells) onto which a catalyst layer can bedeposited is within the scope of the present disclosure. The substrateis positioned at a desired distance from the needle. As will bediscussed in more detail, this distance can be determined or selectedbased at least in part on the physical properties of the chemicalconstituents of the first dispersion.

Step 530 can comprise, for example, placing a substrate on a platform ata position below the first needle of the electrospray apparatus. Invarious embodiments, the distance between the first needle and thesubstrate is between 5 centimeters and 30 centimeters. However, anysuitable distance may be utilized, as desired.

Method 500 further comprises providing a first reservoir of a firstdispersion (step 532). For example, the first dispersion can comprisethe desired chemical components of structured units 106. In variousembodiments, the first dispersion comprises a mixture of catalystparticles (such as catalyst particles 224), carbon-containing supportparticles (such as support particles 222), and an ionomer (such as firstionomer 220 a) in a solvent. Solvents may include, for example, water,alcohols, dimethylformamide, dimethylacetamide, tetrahydrofuran,acetone, ketones, and/or any other suitable solvent or combinationsthereof. In various embodiments, the first dispersion can comprise anadditive or additives, such as those described above.

In various embodiments, method 500 further comprises a step 534 ofapplying an electrical bias between the first needle and the substrate.For example, the substrate can be placed on an electrically conductivemetal plate, such as an aluminum or steel plate. The conductive metalplate and the first needle may be coupled to a power source capable ofapplying an electrical bias between the first needle and the conductiveplate, and therefore, the substrate positioned on the conductive plate.

Method 500 further comprises a step 536 of pumping or otherwisetransferring a first dispersion from a first reservoir through the firstneedle towards the substrate. As previously described, as the firstdispersion exits the needle, the electrical field causes the liquid toform a relatively thin jet that travels toward the substrate.

In various embodiments, method 500 further comprises a step ofevaporating at least a portion of the solvent from the first dispersionprior to the first dispersion contacting the substrate. For example, asthe first dispersion exits the first needle and passes through theelectric field travelling towards the substrate, the solvent canpartially and/or fully evaporate from the dispersion. This evaporationcan solidify the form of structured unit 106. Stated another way, thedispersion forms into the physical core-and-shell structure as ittravels towards the substrate and dries, such that structured unit 106is substantially free of solvent (i.e., contains less than 1 percent ofsolvent) before it contacts the substrate.

The distance between the exit of the first needle and the substrate canbe selected to ensure that most (e.g., above 99 percent) or all of thefirst solvent evaporates before structured units 106 contact thesubstrate. In various embodiments, drying of structured units 106 priorto contacting the substrate and forming catalyst layer 180 can reduce oreliminate cracking in the catalyst layer. Conventionally, cracks form inthe catalyst layer as solvent present in the catalyst layer evaporates.By evaporating most or all of the solvent from a constituent of catalystlayer 180 (i.e., structured units 106), the formation of such cracks incatalyst layer 180 is reduced or eliminated.

With reference now to FIG. 6, another method 600 of forming a catalystlayer of structured units in accordance with various exemplaryembodiments is illustrated. Similar to method 500, method 600 can form acatalyst layer (such as catalyst layer 180), for example a catalystlayer 180 comprising one or more vertically-stacked layers of structuredunits (such as structured units 106).

In various embodiments, method 600 comprises a step 642 of positioning asubstrate relative to a first needle of an electrospray apparatus.Similar to step 530 of method 500, a suitable substrate (such as anexchange membrane or an intermediate substrate) can be positioned belowthe first needle of an electrospraying apparatus at a predetermineddistance. The distance between the first needle and the substrate cancomprise, for example, between 5 centimeters and 30 centimeters, butmore generally any suitable distance.

Method 600 further comprises a step 644 of providing a first reservoirof a first dispersion and a second reservoir of a second dispersion. Forexample, the first dispersion can comprise a mixture of catalystparticles 224, support particles 222, and first ionomer 220 a in a firstsolvent or mixture of solvents. The second dispersion can comprise amixture of catalyst particles 224, support particles 222, and secondionomer 220 b in a second solvent or mixture of solvents. As previouslydescribed, first ionomer 220 a and second ionomer 220 b can be the sameor different from each other. Further, the first solvent and the secondsolvent (or mixtures) can be the same or different from each other. Invarious embodiments, at least one of the first dispersion or the seconddispersion can comprise one or more additives, such as those describedabove.

In various embodiments, method 600 further comprises a step 646 ofapplying an electrical bias between the first needle and the substrate.Similar to step 534 of method 500, step 646 can comprise applying anelectrical bias between the first needle and the conductive plate, andtherefore, to the substrate positioned on the conductive plate.

Method 600 can further comprise a step 648 of pumping or otherwisetransferring the first dispersion from the first reservoir and thesecond dispersion from the second reservoir through the first needletowards the substrate. In various embodiments, the first needle is influid communication with both the first reservoir and the secondreservoir, such that the first dispersion and the second dispersion aremixed as they are pumped through the first needle.

In various embodiments, method 600 further comprises a step 650 ofevaporating solvent from the first dispersion and the second dispersionbefore the dispersions contact the substrate. Similar to step 538 ofmethod 500, the first solvent in the first dispersion and the secondsolvent in the second dispersion are at least partially evaporatedbefore each dispersion reaches the surface of the substrate.

With reference now to FIG. 7, another method 700 of forming a catalystlayer of structured units in accordance with various exemplaryembodiments is illustrated. In various embodiments, method 700 comprisesutilizing two reservoirs, each fluidly coupled to a cannula and aseparate needle.

In various embodiments, method 700 comprises a step 754 of positioning asubstrate relative to a first needle and a second needle of anelectrospray apparatus. Similar to step 530 of method 500, a suitablesubstrate (such as an exchange membrane or an intermediate substrate)can be positioned below a needle (or needles) of an electrosprayingapparatus at a predetermined distance. The distance between theneedle(s) and the substrate can comprise, for example, between 5centimeters and 30 centimeters, and more generally, any suitabledistance.

In various embodiments, the first needle and the second needle arepositioned coaxially relative to each other. For example, the firstneedle may be surrounded coaxially by the second needle. In otherembodiments, the first needle and the second needle are separate fromone another such as, for example, positioned side-by-side.

Method 700 can further comprise a step 756 of providing a firstreservoir of a first dispersion and a second reservoir of a seconddispersion. Similar to step 644 of method 600, the first dispersion cancomprise a mixture of catalyst particles 224, support particles 222, andfirst ionomer 220 a in a first solvent or mixture of solvents. Thesecond dispersion can comprise a mixture of catalyst particles 224,support particles 222, and second ionomer 220b in a second solvent ormixture of solvents. As previously described, first ionomer 220 a andsecond ionomer 220 b can be the same or different from each other.Further, the first solvent and the second solvent (or mixtures) can bethe same or different from each other. In various embodiments, at leastone of the first dispersion and the second dispersion can comprise oneor more additives, such as those described above.

In various embodiments, method 700 further comprises a step 758 ofapplying an electrical bias between the needles and the substrate.Similar to step 646 of method 600, step 758 can comprise applying anelectrical bias between the first needle and the conductive plate andthe second needle and the conductive plate, and therefore, the substratepositioned on the conductive plate.

Method 700 can further comprise a step 760 of pumping or otherwisetransferring the first dispersion from the first reservoir and thesecond dispersion from the second reservoir through their respectiveneedles towards the substrate. Similar to step 648 of method 600, step760 can comprise pumping the first dispersion through the first needleand towards the substrate. Further, as the first dispersion is beingpumped, the second dispersion can be pumped through the second needleand towards the substrate. In such embodiments, in contrast to method600, the first dispersion and the second dispersion do not mix prior toexiting their respective needles.

In various embodiments, method 700 further comprises a step 762 ofevaporating solvent from the first dispersion and the second dispersionbefore the dispersions contact the substrate. Similar to step 650 ofmethod 600, the solvent in the first dispersion at least partiallyevaporates before the dispersion contacts the substrate. Further, thesecond solvent of the second dispersion can at least partially evaporatebefore reaching the surface of the substrate.

Although described with specific reference to one needle (i.e., thefirst needle) or two needles (i.e., the first needle and the secondneedle), methods of forming a catalyst layer in accordance with variousexemplary embodiments can utilize three or more needles, for examplecorresponding with one, two, three, or more dispersions. Additionally, aparticular needle may be used to flow a single dispersion, while anotherneedle may be utilized to flow two or more dispersions mixed thereby.Moreover, the flow rate of a particular dispersion through a particularneedle may differ from the flow rate of another dispersion through thesame needle (and/or differ from the flow rate of another dispersionthrough a different needle). Yet further, an electrical bias appliedbetween a first needle and a substrate may differ from an electricalbias applied between a second needle and the substrate. Additionally,multiple needles and/or combinations of needles may be utilized; forexample, in one embodiment a first dispersion is pumped through a firstneedle toward a substrate while a second dispersion is pumped through asecond needle and a third needle toward the substrate. Still further,characteristics of various needles utilized may differ from one another.For example, a first needle utilized to dispense a first dispersiontoward a substrate may have a first lumen size and/or bevel arrangement,while a second needle utilized to dispense a second dispersion towardthe substrate may have a second, different lumen size and/or bevelarrangement.

With continuing reference to methods 500, 600 and/or 700, processparameters may be varied to achieve desired configurations of structuredunits 106 and or catalyst layer 180. For example, increasing a pump ratecan increase the thickness of shells 210. Moreover, varying the strengthof the electric field and the speed at which the solvent evaporates (forexample, by changing the voltage bias and/or by changing a distancebetween spinnerette and substrate) can change the diameter of structuredunits 106 produced thereby. All such variations, in for example incontinuously variable, alternating, and/or step-wise arrangements orapproaches, are within the scope of the present disclosure. Moreover,structured units 106 (for example, in one or more layers) may beproduced via a first mechanism or process, and thereafter additionalstructured units 106 (for example, in one or more additional layers) maybe deposited thereon via a second, differing mechanism or process.

With reference to FIG. 8, a method 800 of forming an MEA having at leastone catalyst layer of structured units in accordance with variousexemplary embodiments is illustrated. In various embodiments, method 800comprises providing a catalyst layer with a layer of structured units(step 866). For example, a catalyst layer 180 as formed by method(s)500, 600, and/or 700 can be provided for use in forming an MEA.

In various embodiments, method 800 further comprises positioning thestructured units proximate a surface of an exchange membrane (step 868).For example, step 868 can comprise positioning catalyst layer 180 suchthat structured units 106 are proximate and facing a surface of anexchange membrane, such as a proton exchange membrane.

Method 800 can further comprise heat pressing the catalyst layer and theexchange membrane together (step 870). For example, both pressure andheat can be simultaneously applied to the catalyst layer and exchangemembrane to adhere the catalyst layer to the membrane. In someembodiments, heat pressing is performed at a temperature ofapproximately 140 degrees Celsius, for a duration of approximately oneminute, and at a pressure of approximately 4 MPa. However, any suitabletemperatures, durations, and/or pressures may be utilized.

In various embodiments, method 800 further comprises removing thesubstrate from the catalyst layer (step 872). For example, after heatpressing the structured units 106 of the catalyst layer 180 to theexchange membrane, the substrate positioned on the opposing side of thecatalyst layer 180 is no longer needed. That substrate can be removed,such as by peeling, from the opposing side of the catalyst layer 180.

Method 800 can form an electrode and membrane pair, which constitutes aportion of an MEA. In various embodiments, a second catalyst layer isadhered to the side of the membrane opposite the first catalyst layer.The second catalyst layer can comprise structured units 106 havingsimilar structure and/or composition to those of the first catalystlayer. In other embodiments, the second catalyst layer can comprise aconventionally-made catalyst layer, having no structured units 106;moreover, the second catalyst layer may comprise structured units 106differing in configuration from those in the first catalyst layer. Invarious embodiments, heat pressing is applied after a catalyst layer isapplied to each side of the membrane.

TABLE 2 illustrates exemplary and non-limiting operating parameters andcharacteristics of exemplary methods of forming catalyst layers, such asmethods 500, 600, and/or 700. Parameter Range Syringe Pump(s) 1 Rate 0.1mL/h-5 mL/hr Syringe Pump(s) 2 Rate 0.1 mL/h-5 mL/hr Syringe Pump(s) 3Rate 0.1 mL/h-5 mL/hr Length of Needle Tip(s) 1 1 cm-10 cm Distance fromFirst Needle 5 cm-30 cm Distance from Second Needle 5 cm-30 cm VoltageBias 5 kV-60 kV Collection Surface Speed 0.1 m/min-60 m/min Number ofconcentric needles 2-5 Needle Radius 1  0.108 mm-3.810 mm Needle Radius2 0.0826 mm-3.429 mm Air Temperature 15° C.-40° C. Air Relative Humidity5%-100% Environmental gas Air, N₂, Argon Solvent types Water, alcohols,dimethylformamide, dimethylacetamide, tetrahydrofuran, acetone, ketones,fluorinated solvents.

Principles of the present disclosure may be set forth in the followingexample sets, each of which are presented by way of explanation and notof limitation.

Example Set A

Example 1: A structured unit, comprising: an inner core; and an outershell, wherein the inner core has a first radius, wherein the inner corecomprises a plurality of catalyst particles coupled to a plurality ofcarbon-containing support particles and comprises an ionomer at a firstconcentration, wherein the outer shell substantially surrounds the innercore from the first radius to a second radius greater than the firstradius, and wherein the outer shell comprises the ionomer at a secondconcentration greater than the first concentration.

Example 2: the structured unit of Example 1, wherein the structured unitcomprises an overall ionomer to carbon ratio (“I/C ratio”) of between0.5 and 2. Example 3: the structured unit of any of Examples 1-2,wherein the inner core comprises a first I/C ratio, wherein the outershell comprises a second I/C ratio, and wherein the second I/C ratio ishigher than the first I/C ratio. Example 4: the structured unit of anyof Examples 1-3, wherein the structured unit is spherical, and wherein afunction representing the I/C ratio at a series of points that traversebetween the center of the sphere and the outer edge of the sphere has aninflection point at the boundary between the inner core and the outershell.

Example 5: the structured unit of Example 4, wherein the function is asigmoid function. Example 6: the structured unit of Example 4, whereinthe function approximates a step function. Example 7: the structuredunit of any of Examples 1-6, wherein the outer shell has a constantthickness. Example 8: the structured unit of any of Examples 1-6,wherein the outer shell has a variable thickness. Example 9: thestructured unit of any of Examples 1-8, wherein the outer shellcomprises an ionomer not present in the inner core. Example 10: thestructured unit of any of Examples 1-9, wherein the inner core furthercomprises a plurality of support particles, each support particle havinga plurality of catalyst particles adhered thereto.

In this disclosure, reference has been made to the accompanyingdrawings, which form a part hereof, and in which is shown by way ofillustration specific embodiments in which the disclosure may bepracticed. It is understood that other embodiments may be utilized andstructural changes may be made without departing from the scope of thepresent disclosure. References in the specification to “one embodiment,”“an embodiment,” “an example embodiment,” etc., indicate that theembodiment described may include a particular feature, structure, orcharacteristic, but every embodiment may not necessarily include theparticular feature, structure, or characteristic. Moreover, such phrasesare not necessarily referring to the same embodiment. Further, when aparticular feature, structure, or characteristic is described inconnection with an embodiment, it is submitted that it is within theknowledge of one skilled in the art to affect such feature, structure,or characteristic in connection with other embodiments whether or notexplicitly described.

While various embodiments of the present disclosure have been describedabove, it should be understood that they have been presented by way ofexample only, and not limitation. It will be apparent to persons skilledin the relevant art that various changes in form and detail can be madetherein without departing from the spirit and scope of the disclosure.Thus, the breadth and scope of the present disclosure should not belimited by any of the above-described exemplary embodiments, but shouldbe defined only in accordance with the following claims and theirequivalents. The foregoing description has been presented for thepurposes of illustration and description. It is not intended to beexhaustive or to limit the disclosure to the precise form disclosed.Many modifications and variations are possible in light of the aboveteaching. Further, it should be noted that any or all of theaforementioned alternate embodiments may be used in any combinationdesired to form additional hybrid embodiments of the disclosure.

Further, although specific embodiments of the disclosure have beendescribed and illustrated, the disclosure is not to be limited to thespecific forms or arrangements of parts so described and illustrated.The scope of the disclosure is to be defined by the claims appendedhereto, any future claims submitted here and in different applications,and their equivalents. Also, as used herein, the terms “coupled,”“coupling,” or any other variation thereof, are intended to cover aphysical connection, an electrical connection, a magnetic connection, anoptical connection, a communicative connection, a functional connection,a thermal connection, a chemical connection, and/or any otherconnection. When language similar to “at least one of A, B, or C” or “atleast one of A, B, and C” is used in the specification or claims, thephrase is intended to mean any of the following: (1) at least one of A;(2) at least one of B; (3) at least one of C; (4) at least one of A andat least one of B; (5) at least one of B and at least one of C; (6) atleast one of A and at least one of C; or (7) at least one of A, at leastone of B, and at least one of C.

What is claimed is:
 1. A method of forming an electrode, the methodcomprising: providing a first reservoir containing a first dispersion,wherein the first dispersion comprises an ionomer, a carbon-containingcatalyst powder, and a first solvent; providing a second reservoircontaining a second dispersion, wherein the second dispersion comprisesthe ionomer and a second solvent; applying an electrical bias between asubstrate and a first needle in fluid communication with the firstreservoir; and pumping the first dispersion from the first reservoirthrough the first needle towards a first surface of the substrate andpumping the second dispersion from the second reservoir through thefirst needle towards the surface of the substrate to form a plurality ofstructured units on a surface of the substrate, wherein each of thestructured units comprise a spherical inner core having a first radiusand a spherical outer shell having a second radius greater than thefirst radius and concentrically surrounding the inner core, and whereinthe outer shell comprises the ionomer at a first concentration and theinner shell comprises the ionomer at a second concentration that isgreater than the first concentration.
 2. The method of claim 1, whereinthe second needle is positioned coaxially within the first needle. 3.The method of claim 1, wherein a first ratio of the ionomer to carbon atthe first radius of at least one of the structured units is between 0.1and 0.9, and a second ratio of the ionomer to carbon at the secondradius of the at least one of the structured units is between 0.9 and 5.4. The method of claim 1, further comprising evaporating the firstsolvent from the first dispersion prior to the first dispersioncontacting the surface of the substrate.
 5. The method of claim 2,further comprising pumping a third dispersion from a third reservoirthrough one of the first needle or the second needle towards the surfaceof the substrate, wherein the third dispersion comprises the firstionomer, the catalyst powder, and the first solvent.
 6. The method ofclaim 1, wherein the ionomer comprises at least one of perfluorosulfonicacid (PFSA), perfluoro imide acids (PFIA), a quaternary polyphenyleneoxide (QPPO), or a hydrocarbon-based ionomer.
 7. The method of claim 1,wherein the catalyst powder comprises a platinum group metal catalyst.8. A method of forming an electrode, comprising: providing to a firstreservoir a first dispersion comprising a plurality of catalystparticles, a surfactant, a first solvent, and water; providing to asecond reservoir a second dispersion comprising an ionomer and a secondsolvent; applying an electrical bias between the substrate and a firstneedle in fluid communication with the first reservoir and a secondneedle in fluid communication with the second reservoir; pumping thefirst dispersion through the first needle towards a surface of asubstrate; and pumping the second dispersion through the second needletowards the surface of the substrate.
 9. The method of claim 8, whereinthe second needle is positioned coaxially within the first needle. 10.The method of claim 8, further comprising evaporating the first solventprior to contacting the surface of the substrate.
 11. The method ofclaim 8, further comprising evaporating the second solvent prior tocontacting the surface of the substrate.
 12. The method of claim 8,wherein the first dispersion further comprises an additive.
 13. Themethod of claim 12, wherein the additive is a surfactant.
 14. The methodof claim 8, wherein the first solvent comprises a non-polar solvent. 15.The method of claim 8, wherein the second solvent comprises a polarsolvent.
 16. The method of claim 15, wherein the second solventcomprises a mixture of water and an alcohol.
 17. The method of claim 8,wherein the ionomer comprises at least one of perfluorosulfonic acid(PFSA), perfluoro imide acids (PFIA), a quaternary polyphenylene oxide(QPPO), or a hydrocarbon-based ionomer.
 18. The method of claim 8,wherein the plurality of catalyst particles comprises particles of atleast one of a platinum group metal catalyst or a transition-metal-basedn4-macrocyclic metal complex catalyst.
 19. The method of claim 8,wherein the first dispersion further comprises a plurality of ceriumoxide nanoparticles.
 20. The method of claim 13, wherein the firstdispersion comprises a polar solvent, water, and a mixture of thesurfactant and a surfactant solvent, and wherein the second dispersioncomprises water, an alcohol, and PFSA.